Enhance needless_late_init to cover grouped assignments (#16746)

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comments](https://triagebot.infra.rust-lang.org/gh-comments/rust-lang/rust-clippy/pull/16746)*

Closes #16330

Implemented as an enhancement to `needless_late_init`. Also fixes a FN
when if/match is in block expr.

changelog: [`needless_late_init`] fix FN for if/match in block expr
changelog: [`needless_late_init`] extend to cover grouped assignments

Author: rustbot

CHANGELOG.md

@@ -7574,6 +7574,7 @@ Released 2018-09-13
 [`avoid-breaking-exported-api`]: https://doc.rust-lang.org/clippy/lint_configuration.html#avoid-breaking-exported-api
 [`await-holding-invalid-types`]: https://doc.rust-lang.org/clippy/lint_configuration.html#await-holding-invalid-types
 [`cargo-ignore-publish`]: https://doc.rust-lang.org/clippy/lint_configuration.html#cargo-ignore-publish
+[`check-grouped-late-init`]: https://doc.rust-lang.org/clippy/lint_configuration.html#check-grouped-late-init
 [`check-incompatible-msrv-in-tests`]: https://doc.rust-lang.org/clippy/lint_configuration.html#check-incompatible-msrv-in-tests
 [`check-inconsistent-struct-field-initializers`]: https://doc.rust-lang.org/clippy/lint_configuration.html#check-inconsistent-struct-field-initializers
 [`check-private-items`]: https://doc.rust-lang.org/clippy/lint_configuration.html#check-private-items

book/src/lint_configuration.md

@@ -452,6 +452,37 @@ For internal testing only, ignores the current `publish` settings in the Cargo m
 * [`cargo_common_metadata`](https://rust-lang.github.io/rust-clippy/master/index.html#cargo_common_metadata)
 
 
+## `check-grouped-late-init`
+Whether to check for grouped late initializations from multiple `let` statements.
+
+#### Example
+```rust
+let a;
+let b;
+if true {
+    a = 1;
+    b = 2;
+} else {
+    a = 3;
+    b = 4;
+}
+```
+Use instead:
+```rust
+let (a, b) = if true {
+    (1, 2)
+} else {
+    (3, 4)
+};
+```
+
+**Default Value:** `true`
+
+---
+**Affected lints:**
+* [`needless_late_init`](https://rust-lang.github.io/rust-clippy/master/index.html#needless_late_init)
+
+
 ## `check-incompatible-msrv-in-tests`
 Whether to check MSRV compatibility in `#[test]` and `#[cfg(test)]` code.
 

clippy_config/src/conf.rs

@@ -554,6 +554,30 @@ define_Conf! {
     /// For internal testing only, ignores the current `publish` settings in the Cargo manifest.
     #[lints(cargo_common_metadata)]
     cargo_ignore_publish: bool = false,
+    /// Whether to check for grouped late initializations from multiple `let` statements.
+    ///
+    /// #### Example
+    /// ```rust
+    /// let a;
+    /// let b;
+    /// if true {
+    ///     a = 1;
+    ///     b = 2;
+    /// } else {
+    ///     a = 3;
+    ///     b = 4;
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// let (a, b) = if true {
+    ///     (1, 2)
+    /// } else {
+    ///     (3, 4)
+    /// };
+    /// ```
+    #[lints(needless_late_init)]
+    check_grouped_late_init: bool = true,
     /// Whether to check MSRV compatibility in `#[test]` and `#[cfg(test)]` code.
     #[lints(incompatible_msrv)]
     check_incompatible_msrv_in_tests: bool = false,

clippy_lints/src/lib.rs

@@ -731,7 +731,7 @@ rustc_lint::late_lint_methods!(
         UndocumentedUnsafeBlocks: undocumented_unsafe_blocks::UndocumentedUnsafeBlocks = undocumented_unsafe_blocks::UndocumentedUnsafeBlocks::new(conf),
         FormatArgs: format_args::FormatArgs<'tcx> = format_args::FormatArgs::new(tcx, conf, format_args.clone()),
         TrailingEmptyArray: trailing_empty_array::TrailingEmptyArray = trailing_empty_array::TrailingEmptyArray,
-        NeedlessLateInit: needless_late_init::NeedlessLateInit = needless_late_init::NeedlessLateInit,
+        NeedlessLateInit: needless_late_init::NeedlessLateInit<'tcx> = needless_late_init::NeedlessLateInit::new(conf),
         ReturnSelfNotMustUse: return_self_not_must_use::ReturnSelfNotMustUse = return_self_not_must_use::ReturnSelfNotMustUse,
         NumberedFields: init_numbered_fields::NumberedFields = init_numbered_fields::NumberedFields,
         ManualBits: manual_bits::ManualBits = manual_bits::ManualBits::new(conf),